Implantable heart stimulator

ABSTRACT

An implantable heart stimulator has an electrically conductive housing containing a pulse generator, with an electrode lead connected to the housing. The electrode lead has a proximal portion extending substantially from the housing to a location, after implantation, which is beyond the entry of the lead into the venous system and before the entry of the lead into the superior vena cava. A current source supplies an infection control current between the housing and an electrically conductive surface on the exterior of the proximal portion of the electrode lead, for counteracting bacterial growth. The housing may have a header to which the electrode lead is connected, in which case the header is provided with an electrically conductive surface as well, which can serve as an electrode for the infection control current.

TECHNICAL FIELD

[0001] The present invention relates to an infection control apparatus for an implantable heart stimulator comprising a pulse generator for delivering electric stimulation pulses to a patient's heart through a lead connectable to said pulse generator, possibly through a connector top on a pulse generator housing, said pulse generator housing being electrically conductive.

BACKGROUND

[0002] Implantable heart stimulator pocket infection is a severe complication which often ends up in explantation of the stimulator. The reason therefor is that conventional treatment with antibiotics cannot eradicate the infection. This seems to depend on the circumstance that the bacteria live in a biofilm formed around the exterior surfaces of the implanted stimulator, which film blocks antibiotica. The bacteria may also live passively on a very low metabolism and can therefore not be treated successfully by antibiotica.

[0003] A method of enhancing the effect of antibiotica by applying an electrical field across the biofilm is described in U.S. Pat. No. 5,312,813. This method is based on findings by J. W. Costerton et. al. Their studies have shown that the infection can be completely cured and no explantation has to take place by applying an electric field or a small current across the biofilm during antibiotic treatment, cf. also ASAIO Journal 1992, p.M174-M178, Khoury et. al, “Prevention and Control of Bacterial Infections Associated with Medical Devices”, and Antimicrobial Agents and Chemotherapy, Vol.38, No. 12, December 1994, p.2803-2809, Costerton et. al., “Mechanism of Electrical Enhancement of Efficacy of Antibiotics in Killing Biofilm Bacteria”. In these studies, generally, a low electric current of the order of 15-400 μ/cm² is applied onto the infected surface while they were immersed in a buffer with antibiotica. In the most successful studies a total killing of microorganisms was reported after only 8 hours of current and antibiotic treatment—tobramycin 2.5 mg/l, 15-400 μA/cm², during 8 h. This effect has been termed “the bioelectric effect”.

[0004] These studies suggest that the electric field need to be applied in close proximity to the infected implant. A possible explanation to the observed effect is that electrochemically generated products are needed for the bioelectric effect to occur. At the titanium surface, titanium being normally used in heart stimulator housings, the following electrochemical processes take place.

[0005] At the anode:

[0006] 1) 2H₂O→O₂+4H⁺+4e⁻

[0007] 2) 2Cl⁻→Cl₂+2e⁻

[0008] 3) Ti⁺2H₂O→TiO₂+4H⁺+4e⁻

[0009] At the cathode:

[0010] 1) O₂+2H₂O+4e⁻→4OH⁻

[0011] 2) 2H₂O+2e⁻→H₂+2OH⁻

[0012] It is supposed that primarily the produced oxygen and chloride gases have an influence on the biofilm attached to the surface. It is also supposed that the fact that the pH-value is lowered at the anode and increased at the cathode is significant for the influence and viability of the biofilm.

[0013] An infection that is initiated in the stimulator pocket will also often start to spread along the lead. The polymer surface of the lead may be a substrate for the bacteria and makes it easy for the bacteria to attach. At the time when a pocket infection is clinically manifested, in many cases the infection has already spread some distance from the stimulator pocket along the lead.

[0014] As the bioelectric effect is concentrated to parts in conjunction with or in close proximity to conducting surfaces of the implant, it is one purpose of the present invention to extend these conducting active surfaces.

DISCLOSURE OF THE INVENTION

[0015] This purpose is obtained by an apparatus of the type defined in the introductory portion and having the characterising features of claim 1.

[0016] As discussed above the bioelectric effect is limited to conducting surfaces of the implanted device or to the immediate proximity thereof. With the present invention a design is obtained which makes it possible to extend the bioelectric effect to traditionally non conducting surfaces of an implanted heart stimulator, like a pacemaker or a cardioverter-defibrillator (ICD). By making also exterior surfaces of the proximal part of the lead and a possible connector top electrically conductive all exterior stimulator surfaces located within the subcutaneous implant pocket and a part of the lead extending from the pocket are electrically conductive, and by adapting these electrically conductive surfaces to form at least two separate electrodes and providing a current source to supply an electric infection control current between these electrodes all exterior surfaces will be current coated, and the bioelectric effect will be extended to all surfaces within the pocket and also to the exterior surface of the proximal part of the lead. By making the normally non-conducting surfaces of the connector top and the lead electrically conducting not only effective treatment of infections within the pocket is possible, but spreading of the infection from the pocket along the lead is prevented. The lead will in this way benefit from the bioelectric effect and thus it is prevented that bacteria reach the endocardium giving rise to endocarditis.

[0017] According to an advantageous embodiment of the apparatus according to the invention an electrically conducting polymer is applied on said exterior surfaces of the proximal part of said lead and said possible connector top. In this way traditionally non-conducting surfaces of a heart stimulator are made electrically conductive. An example of a polymer suitable for this purpose is an electrically conducting polymer marketed under the trademark ELASTOSIL.

[0018] According to another advantageous embodiment of the apparatus according to the invention an electrically conducting coil is applied around said proximal part of the lead. In this way the proximal part of the lead is made not only electrically conductive but the wear resistance of the lead is improved.

[0019] According to still another advantageous embodiment of the apparatus according to the invention the exterior surfaces of the proximal part of the lead and of said possible connector top are treated by ion implantation technology or so-called Ion-Beam-Assisted-Deposition. This technique is especially well suited for making stimulator connector tops or headers of epoxy electrically conductive.

[0020] Other possible technologies to make a surface conducting are Physical Vapor Deposition, PVD, or Chemical Vapor Deposition, CVD or any sputtering process.

[0021] It has been found that oxide layers, especially titanium oxide layers but also other metal oxide layers may be formed when such metals are used in the DC current environment dealt with in conjunction with the present invention. These oxide layers may cause an uneven current distribution possibly detrimental to the infection control effect. The current may also be lowered due to increased impedance caused by the oxide layer to a point at which the effect on bacteria in the biofilm is no longer effective. The formation of such oxide layers is avoided, according to an advantageous embodiment of the apparatus according to the invention, by coating the generator housing and other metallic surfaces that may become oxidized due to the DC current with one of the metals platinum, palladium or iridium or any other metal with similar electrochemical characteristics or an alloy of these metals.

[0022] According to an embodiment of the apparatus according to the invention the current source is formed of an electric pulse generator battery. Thus in case of heart stimulators, like pacemakers or ICDs, having their own energy source, no external source will be required.

[0023] According to another advantageous embodiment of the apparatus according to the invention means are provided to inductively couple an externally located current source to the electrodes thereby avoiding loading of the internal battery.

[0024] According to other advantageous embodiments of the apparatus according to the invention the inductive coupling means comprise a single layer inductive coil attached to the outer surface of the pulse generator housing and electrically connected to the electrodes or an inductive coil positioned inside the pulse generator housing and electrically connected to the electrodes. Such single layer coils, which are manufactured preferably by screen printing, will not require much space and will consequently contribute to a compact stimulator construction. A rectifying means is connected between said coil and one of the electrodes to supply a DC current to the electrodes. Such a coil might also be used as a telemetry coil.

[0025] According to still another advantageous embodiment the connector top and the pulsegenerator housing are adapted to be in mechanical contact with transcutaneously inserted needles that inject the infection control current from a current source located outside the patient's body.

[0026] The present invention also relates to a heart stimulator comprising a pulse generator for delivering electric stimulation pulses to a patient's heart through a lead, connectable to said pulse generator, possibly through a connector top on a pulse generator housing, said pulse generator housing be electrically conductive, which stimulator is characterised by an apparatus as disclosed above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] To explain the invention in greater detail embodiments of the apparatus according to the invention will now be described with reference to the drawings, on which

[0028]FIG. 1 shows schematically a heart stimulator with a lead provided with a coil on its proximal part,

[0029]FIG. 2 shows an embodiment with pulse generator housing serving as a first electrode and lead and connector top serving as a second electrode, and

[0030]FIG. 3 shows schematically a heart stimulator with a surface mounted coil on the exterior of the stimulator housing for inductively connecting an external current source to the electrode forming parts of the implant.

[0031]FIG. 4 shows an embodiment in which the infection control current is delivered from an external current source via transcutaneous electrodes.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0032] In the apparatus according to the invention a. o. the proximal part of the lead extending to a position which after implantation of the lead is situated between a location beyond the entry into the venous system and the entry into vena cava superior, is made electrically conductive. This can be realised in several different ways. Thus the proximal part can be made electrically conductive by e.g. applying an electrically conducting polymer on its surface or by other techniques, previously described such as ion implantation technology, Ion-Beam-Assisted-Deposition (IBAD). In FIG. 1 another example of making a proximal lead part electrically conductive is shown.

[0033]FIG. 1 shows schematically an implantable heart stimulator 2 having a connector top 4 to which a lead 6 is connected. The proximal part of the lead 6 is made electrically conductive by wrapping a metallic coil 8 around this part of the lead. The metallic coil 8 will also improve the wear resistance of the lead 6.

[0034] The connector top or header 4 is often made of epoxy and IBAD or any of the previously described techniques is suitable for making such a connector top conductive.

[0035]FIG. 2 shows an embodiment with an electrically conductive stimulator housing, an electrically conductive connector top 12 and a lead 14 with an electrically conductive proximal part 16. The pulse generator housing 10, which normally is made of titanium, serves as a first electrode and is isolated from the connector top 12 and the lead 14, which are forming a second electrode. The electrically conductive proximal part 16 of the lead 14 is extending to a position which after implantation of the lead is situated between a location beyond the entry into the venous system and the entry into vena cava superior. With this embodiment it is secured that all exterior surfaces of the implanted stimulator receive adequate therapy by connecting a current source (not shown in the figure) in any suitable way to the electrodes.

[0036] Of course generator housing, connector top and proximal part of the lead can be divided into two separate electrodes in a number of other ways. Thus, e.g. generator housing and connector top can form one electrode, while the proximal part of the lead is forming the other, and also other combinations are obvious. It is important, however, that the electrodes are designed such that the current distribution for the bioelectric effect is as uniform as possible across the exterior surfaces.

[0037]FIG. 3 shows schematically an embodiment for generating current for electric infection control by electromagnetic induction. Thus a super thin surface mounted coil 18 is attached to the exterior surface of the stimulator housing 20. This coil 18 can be manufactured by e.g. screen printing. A polymeric isolation film 22 is provided to electrically isolate the coil 18 from the stimulator housing 20.

[0038] One end 24 of the coil 18 is electrically connected to the housing 20, while the other end is connected to a diode 26 integrated in the epoxy connector head 28. The diode 26, in its turn, is connected to a counter electrode 30 at the external surface of the connector head 28.

[0039] By applying a high frequency electromagnetic field by an external energy source located in the proximity of the stimulator, a current will be generated in the coil 18. The diode 26 will allow current in only one direction and thus permit the electrochemical processes necessary for the bioelectric effect to occur. As an alternative, the coil can be placed inside the stimulator housing. One end of the coil is then connected to the stimulator housing, whereas the other end of the coil is connected via a diode to an external counter electrode, preferably integrated in the epoxy connector head.

[0040]FIG. 4 shows schematically the implanted pulse generator in the patient. The conductive connector top 4 and the proximal conductive portion 8 of the lead 6 form one electrode and the casing 2 of the pulse generator form the other electrode. The external infection control current source 31 is connected to the conductive connector top and the pulse generator casing via transcutaneous electrodes 29,30 

1. An infection control apparatus for an implantable heart stimulator comprising a pulse generator for delivering electric stimulation pulses to a patient's heart through a lead (6,14) connectable to said pulse generator, possibly through a connector top (4,12, 28) on a pulse generator housing (2,10,20), said pulse generator housing (2,10,20) being electrically conductive, characterized in that the exterior surfaces of said possible connector top (4,12,28) and of a proximal part (8,16) of the lead (6,14) are electrically conductive, said proximal part extending to a position which after implantation of the lead is situated between a location beyond the entry into the venous system and the entry into vena cava superior, said generator housing (2,10,20) and said electrically conductive surfaces of said proximal lead part and of said possible connector top being adapted to form at least two separate electrodes, and in that a current source is provided to supply an electric infection control current between said electrodes.
 2. The apparatus according to claim 1, characterized in that said exterior electrically conductive surfaces are formed from a conducting polymer.
 3. The apparatus according to claim 1, characterized in that said exterior electrically conductive surface of the proximal part of the lead is comprised of an electrically conductive coil.
 4. The apparatus according to claim 1, characterized in that said exterior electrically conductive surfaces are formed through a treatment by ion implantation technology or so-called Ion-Beam-Assisted-Deposition.
 5. The apparatus according to claim 1, characterized in that said exterior electrically conductive surfaces are formed through coating with a vapor deposition or sputtering process.
 6. The apparatus according to any of the preceding claims, characterized in that said generator housing (2,10,20) is coated with one of the metals platinum, palladium or iridium or any other metal with similar electrochemical chararecteristics, or an alloy of these metals.
 7. The apparatus according to any one of the preceding claims, characterized in that said pulse generator housing (2,10) is forming one of said electrodes and is electrically isolated from said proximal part (8,16) of the lead (6,14) and possible connector top (4,12) which are forming the other electrode.
 8. The apparatus according to any one of the claims 1-7, characterized in that said current source is formed of an electric pulse generator battery.
 9. The apparatus according to any one of the claims 1-7, said current source being externally located, characterized in that means (18) are provided to inductively couple said externally located current source to said electrodes.
 10. The apparatus according to claim 9, characterized in that said inductive coupling means comprise a thin inductive coil (18) attached to the outer surface of the pulse generator housing (20) and electrically connected to the electrodes.
 11. The apparatus according to claim 9, characterized in that said inductive coupling means comprise an inductive coil positioned inside the pulse generator housing and electrically connected to the electrodes.
 12. The apparatus according to claim 9-11, characterized in that a rectifying means (26) is connected between said means or said coil and one of the electrodes to supply a DC current to the electrodes.
 13. The apparatus according to claim 1-6, characterized in that an external infection control current source (31) is connected to the housing (2) and connector top (4) via transcutaneous electrodes (29,30).
 14. A heart stimulator comprising a pulse generator for delivering electric stimulation pulses to a patient 's heart through a lead, connectable to said pulse generator, possibly through a connector top (4,12,28) on a pulse generator housing, said pulse generator housing (2,10,20) being electrically conductive, characterized by an apparatus according to any one of the preceding claims. 